This invention relates to devices for centrifugal filtering of fluid samples, and to filter units for such devices.
The analysis of relatively small fluid samples for industrial, medical and other purposes commonly requires, as a preliminary step, separation of solid and liquid components of a sample by microfiltration. It is known to perform such filtration by a procedure herein termed centrifugal filtering, viz. by placing the sample in one end of a tubular device which is divided transversely by a microfilter and spinning the device in a centrifuge so as to force the liquid of the sample through the filter into the other end of the device, for subsequent removal and analysis, solid components of the sample being retained on the filter. Centrifugal filtering affords advantages, notably including rapidity of filtering action and ability to prepare multiple samples simultaneously, over other types of filtering methods.
There is an increasing demand in the area of analytical chemistry for filtration devices capable of handling moderate (e.g. 5 ml) to small (e.g. 20 .mu.l) samples of great value, in a manner which is rapid, gives high recovery, and minimizes any possibility of sample contamination. Among other specific desired attributes of a centrifugal filtering device are capability of enabling facile recovery of solid components separated from the liquid of a sample by the filtering operation (so that the solids, as well as the liquids, can be analyzed); low cost and ease of manufacture; simplicity of handling by the user; and suitability for use in conventional centrifuges. Moreover, along with increasing instrument sensitivity, speed of processing throughput, and dedicated component detection and quantitation, has come an increasing need for prior sample preparation techniques providing means for rapid sampling, desalting, and buffer exchange, or prepurification (selective removal of specific components or groups of components to eliminate possible interference in the analytical detection of the remaining components or to retain such components for eventual recovery in concentrated form), to obtain a sample in the most suitable form for instrumental analysis. Desirably, centrifugal filtering devices should not only be designed to carry out the functions of general filtration (separation and isolation of solid and liquid components one from another) but should also be sufficiently versatile for use in these more demanding and sophisticated types of sample preparation required by present-day high resolution instrumentation.